A. Field of the Invention
This invention pertains to dc power supplies, and more particularly to switched dc power supplies having circuitry constructed and arranged to eliminate ripple on the output.
B. Description of the Prior Art
Switched dc power supplies have become popular in a large number of applications as a means of providing an efficient and reliable power source of substantially any desired voltage and power requirements. While in many of these applications, a ripple of relatively large amplitudes can be tolerated, in other applications, the ripple must be minimized. This consideration is important, for example for power sources used in remote locations, or power supplies used to provide power to a remote, and often inaccessible location, where the leads from the power source to the load is use secondarily for a second function, such as, for example, communications. In these applications, the ripple on the output must be reduced so that it will not interfere with the communication channel. However, the inventors have found that it is virtually impossible to eliminate theh ripple completely using standard single or multi-stage filters because of resulting equivalent series resistance (ESR).
Earlier attempts at resolving this problem can be seen, for example, in Technical Support Package entitled, "Reducing Ripple in a Switching Voltage Regulator", NASA Tech Briefs GSC-13594. While this document suggests a current injection scheme for reducing ripple at the output of switching voltage regulator, fails to appreciate the effects of the ESR on ripple, and erroneously states that the effects of ESR are neglibible.